Dorset sheep with accurately timed gestations are used under aseptic surgical conditions. Cannula, thermisters, and electromagnetic flow probes are placed into both material and fetal circulations as well as the intact outer sac. Using a postoperatively recovered chronic sheep preparation, maternal hyperthermia is induced by the combined use of increased humidity and increased ambient temperature. Measurements of effects of this environmental change on maternal and fetal endocies are measured.